Offset of a Landmass

Old Guy

I am trying to use the offset command to generate an offset from my coastline, but it is not working as I expected. Should I be using something other than offset?

What happens looks like it is exploding the polygon, offsetting each line individually, and then recombining all of those offset lines into a new polygon. I'm sure that's not what it is doing but that is the best way I can think of to describe what it looks like. Any suggestions?

Old Guy

Here is an example with an exaggerated coastline and a large offset to emphasize the problem.

Ralf

Offset will have problems with entities with lots of nodes and especially inside curves. As the offset expands the nodes, they will encroach and overlap another, resulting in the weird mess you see. You can try to mitigate this by doing several small offsets in a row and deleting offending nodes in between the offsets, but it'll usually be quicker to just draw an outline around the coast by hand.

Offset is best used with simpler and more regular entities. It's great for creating regular patterns and similar things, but not for outlining complex shapes.